Gonads 2

Question 1

What two reactions can testosterone follow and what do they produce?

Answer 1

Testosterone —> Oestrogen (aromatisation: by the action of aromatase)
Testosterone —> Dihydrotestosterone (reduction)
Dihydrotestosterone is a more potent androgen that binds to the same androgen receptors as testosterone.

Question 2

What is needed for male phenotypic appearance?

Answer 2

Dihydrotestosterone (DHT)

Question 3

Transport of lipophilic (sex) hormones

Answer 3

Must be bound to carrier protein in the blood

Question 4

How is testosterone found in the blood?

Answer 4

60% testosterone and DHT are linked to Sex hormone binding globulin (SHBG),
38% testosterone and DHT is bound to Albumin
2% remains “free”

Question 5

How is testosterone found in seminiferous fluid and semen?

Answer 5

Bound to Androgen binding globulin (ABG)

Question 6

What are the 2 principal actions of Androgens in a foetus?

Answer 6

Development of male internal and external genitalia
Fetal growth (acting with other hormones)

Question 7

What are the 5 principal actions of Androgens in an adult?

Answer 7

Needed for spermatogenesis
Growth and development of:
Male genitalia
Secondary sex characteristics e.g. facial hair
Protein and bone anabolism i.e. muscle / bone growth
Behavioural: Male sexual behaviour
Pubertal growth spurt (with GH)

Question 8

Some ‘androgenic’ effects (of testosterone) in men are mediated by conversion to oestrogen: example

Answer 8

Testosterone affects male sexual behaviour in the brain by being converted to oestrogen in the brain

Question 9

Oestrogens

Answer 9

Any substance (natural or synthetic) which induces mitosis in the endometrium (womb thickening)

Question 10

Name 3 oestrogens

Answer 10

17 Beta-Oestradiol (main oestrogen in women)
Oestrone (precursor)
Oestriol (main oestrogen produced in pregnancy)

Question 11

5 reproductive effects of oestrogens

Answer 11

ENDOMETRIUM: Stimulates proliferation (mitosis) i.e. womb thickening
MENSTURAL CYCLE: Triggers LH surge resulting in ovulation
Vagina / Cervix: secretions
Breasts: Stimulates growth of ductile system
Skin: Decreases sebaceous gland secretion

Question 12

7 non-reproductive effects of oestrogens

Answer 12

Feedback regulation on GnRH (negative and positive)
Stimulates osteoblasts
Metabolic actions (e.g. on lipids)
Behavioural effects
Increases salt (and water) reabsorption
Increases plasma protein synthesis (hepatic effect)
Influences the release of other hormones (e.g. prolactin, thyrotrophin)

Question 13

Progestogens

Answer 13

Any substance (natural or synthetic) inducing secretory changes in the endometrium (Allowing an embryo to implant)

Question 14

Name 2 Progestogens

Answer 14

Progesterone

17 Alpha-hydroxyprogesterone

Question 15

List 5 effects of Progestogens

Answer 15

Stimulates secretory activity in endometrium and cervix (to prepare for implantation of embryo)
Negative feedback regulation on hypothalamic GnRH
Increase in basal body temperature
Decreases renal NaCl re-absorption (competitive inhibition of aldosterone)
Stimulates growth of alveolar system in breast

Question 16

What hypothalamic hormone stimulates FSH and LH release from the pituitary gland? How often are pulses of it released?

Answer 16

Gonadotrophin Releasing Hormone (GnRH)

Released in pulses~ every hour

Question 17

Which cells in the testes have receptors for FSH and LH? How do they respond?

Answer 17

FSH: Sertoli Cells; support spermatogenesis and produce inhibin
LH: Leydig Cells; make testosterone (virilises men)

Question 18

Describe the negative feedback from the testes to hypothalamo-pituitary axis.

Answer 18

Sertoli Cells: produce INHIBIN: negative feedback effect on hypothalamus and pituitary
Leydig Cells: produce TESTOSTERONE: negative feedback effect on hypothalamus and pituitary

Question 19

What does sperm maturation require?

Answer 19

Testosterone

Question 20

How do testosterone and inhibin cause negative feedback?

Answer 20

Decreases the AMPLITUDE of the GnRH pulses.

Question 21

Describe the local positive feedback loop in the ovaries.

Answer 21

FSH stimulate aromatase and increases conversion of androgens to 17 beta oestradiol.
Oestrogen then leaves the granulosa cell and binds to oestrogen receptors on the SAME granulosa cell and further stimulates production of oestrogen.

Question 22

What are the effects of LH and FSH on the ovaries?

Answer 22

Make ovaries release Oestradiol and Inhibin

Question 23

Describe the early follicular phase

Answer 23

1st 5 days of cycle
5-10 eggs start to enlarge and grow
Compete with each other (Winner= Graafian follice)
Grow under influence of FSH
Follicles start producing 17 Beta-Oestradiol (+ a tiny bit of progesterone, which is converted to 17 Beta-Oestradriol)
As follicles are very small, relatively small amounts of
17 Beta-Oestradiol is produced

Question 24

Describe the early-mid follicular phase

Answer 24

17 Beta-Oestradiol starts to increase due to increasing size of follicles (due to stimulation from LH and FSH)
One of the follicles gets bigger than the others
Bigger follicle produces more 17 Beta-Oestradiol
In this follicle you get a local (autocrine) positive feedback loop:
Rising plasma E2 stimulates granulosa cells around it to grow more
Able to make more E2

Question 25

Describe the mid follicular phase

Answer 25

E2 levels pretty high Starts to “starve off” supply of LH and FSH from pituitary This kills off all of the other follicles

Question 26

Most developing follicles will then undergo atresia and only one follicle remains, the Graffian follicle. What enables this follicle to survive the negative feedback on FSH?

Answer 26

Graffian follicle is no longer FSH-dependent and can survive with it's own local production of oestrogen. The other cells are FSH-dependent and so undergo atresia when the FSH is removed.

Question 27

Describe the late follicular phase

Answer 27

Extremely high E2 from Graafian Follicle triggers positive feedback in hypothalamus and pituitary on GnRH / LH secretion i.e. LH surge / ovulation Pituitary gets “Activated” = LH Surge Causes follicle to break open and egg to move down fallopian tube to uterus

Question 28

What is the difference between the 2 populations of GnRH neurones in the hypothalamus?

Answer 28

1 is negatively fedback (Normal levels) | 1 is positively fedback (Under extremely high levels of E2)

Question 29

Describe the luteal phase

Answer 29

Corpus luteum makes progesterone | Progesterone prepares the endometrium for implantation: converts lining to secretary lining

Question 30

If fertilisation does not occur, what happens?

Answer 30

Oestradiol, Progesterone and Inhibin have negative feedback effect on FSH and LH leading to luteolysis and menstruation.

Question 31

What is the difference between primary and secondary amenorrhoea?

Answer 31

Primary: never had a period Secondary: used to have period but then they stopped

Question 32

Define infertility.

Answer 32

Couple cannot get pregnant following 12 months of regular unprotected sex Woman: inability to get pregnant Man: inability to impregnate

Question 33

Define amenorrhoea

Answer 33

Absence of menstrual cycles

Question 34

Define Oligomenorrhoea

Answer 34

Infrequent cycles. | Less severe than amenorrhoea

Question 35

List 5 causes of infertility

Answer 35

Pituitary failure: won’t make LH and FSH Prolactinoma: Form of pituitary tumour, make prolactin, inhibits LH and FSH Testicular failure e.g. mumps, Klinefelter syndrome (XXY) Ovarian failure e.g. Turner syndrome (XO) Polycystic ovarian syndrome (PCOS)

Question 36

List 3 characteristics of Polycystic ovarian syndrome (PCOS)

Answer 36

Infrequent periods Hyper-androgenaemia e.g. increased male pattern hair, acne Polycystic ovaries (increased number of enlarging ovarian follicles)